1. Field of the Invention
The present invention relates to display of power supply in a display apparatus having display unit with memory properties.
2. Description of the Related Art
Commonly used conventional display apparatuses include CRTs and TN type or STN type liquid crystal displays. Display on those display apparatuses disappears when the supply of power is stopped.
However, bistable ferroelectric liquid crystals have recently been developed and put in use in display apparatuses. Such ferroelectric liquid crystals have memory properties and are characterized in that they keep on displaying even if the supply of power is stopped after a display is presented. Therefore, it is only required to supply power to a display apparatus, for example, only when a display is changed, and the supply of power can be stopped while the user is looking at the display, which makes it possible to achieve a significant reduction of power consumption. For example, they may be loaded on battery-driven apparatuses and the like, and they can provide a long life even in such a case.
However, users are accustomed to the fact that a display disappears when the supply of power is stopped by their experiences. For example, this has resulted in a problem in that a user may not be aware of dead batteries when a display apparatus having memory properties keeps on displaying. Specifically, even when batteries die, the user may believe that the batteries are still alive because the display is still maintained. For example, in the case of an apparatus that receives information to be displayed from outside, even when the reception of information has been disabled by dead batteries, the user may believe that information has been received without becoming aware of the fact or may suspect the apparatus to be defective because of the disabled reception. In addition, since the apparatus may be randomly and repeatedly operated in such a state, the consumption of the batteries is further accelerated.
Further, although a voltage drop causes a display to stay unchanged even if the apparatus is operated, the user may misunderstand the same state as a trouble of the apparatus instead of recognizing the dead batteries. Furthermore, since a display is maintained even when the batteries are removed, the user may even be unaware of the fact that the batteries have been removed. A problem arises when batteries are inserted in verse in that the restoration of a normal state can not be recognized because there is no change in a display.
In consideration to such problems, for example, according to Japanese patent No. 2670045, Japanese Patent Laid-Open Nos. H6-4041 and H6-4047 and the like, a unit for detecting a power supply off state is provided, and a screen is initialized by an initializing unit when it is detected that the power supply is off. According to the disclosure of Japanese Patent Laid-Open No. H8-110511, a unit for detecting a power supply off sate similar to those in the above-mentioned articles is provided, and a voltage for turning off a displayed screen is applied for a period corresponding to one frame or more when it is determined that the power supply is off. According to any of those articles, since a display on an apparatus is turned off when the power supply is turned off, a user can operate the apparatus with operability similar to that of conventional display apparatuses such as CRTs. However, this eliminates the advantage in that a display is saved even when the power supply is turned off.
Japanese Patent Laid-Open No. H6-274120 discloses a technique in which characteristics of a display having memory properties are utilized to preserve a state of the display as it is when a drop of the power supply voltage attributable to runaway of a computer, circuit abnormality or the like is detected. This makes it possible to easily store and maintain the contents of a display immediately before the occurrence of abnormality. Further, Japanese Patent Laid-Open No. H8-160385 discloses a display apparatus in which system information is always displayed in a display area to allow information that has been displayed when the power supply is interrupted to be displayed at a low cost after the interruption of the power supply or when the power supply is turned on again utilizing memory properties of the display area.
In those apparatuses, however, although a display can be maintained at the time of the interruption of the power supply, the user can not recognize dead batteries or the like as described above because the display is maintained. According to those articles, therefore, no solution is proposed for the problem of users"" inability to know the state of batteries as described above.
The invention has been made taking the above-described situation into consideration and provides a display apparatus which utilizes a display unit having memory properties and which notifies a user of a low battery level, the absence of the batteries, the restoration of a normal voltage as a result of reloading of the batteries, and the like.
According to the invention, there is provided a display apparatus having a display unit having memory properties, a control unit which causes the display unit to display information and a battery which supplies power to each part, characterized in that the control unit causes the display unit to display that the battery is dead when the amount of energy of the battery is reduced and causes it to maintain the display indicating the dead battery utilizing the memory properties of the display unit. The display indicating the dead battery can be presented using a part or the entirety of a display screen, and a method for replacing the battery can be displayed. With such a configuration, even if a display is maintained on the display unit when the battery is dead, the user can recognize the fact that the battery is dead because the display indicating the dead battery is presented. A reduction of the amount of energy of the battery can be detected from a drop of the voltage of the same below a predetermined voltage.
In the case of a reduction of the amount of energy of the battery (e.g., a voltage drop), the screen display may be disturbed when the display is updated thereafter. Under such circumstances, for example, the display unit may be controlled such that it does not update a display even when it receives an instruction from the user until the battery is replaced after a display is presented to indicate the fact that the battery is dead. In this case, when the display apparatus performs operations other than displaying, e.g., a function of receiving information to be displayed from the outside, the reception of information can be continued.
Further, the battery can be removed for reasons other than a reduction of the amount of energy thereof as a result of consumption. In order to cope with such a situation, a capacitor unit can be provided which stores power to allow at least a part of the display unit to be rewritten when the battery is removed. A display indicating the removal of the battery is presented on a part or the entirety of the display screen of the display unit while power is being supplied from the capacitor unit in the absence of the battery. At this time, the display indicating the removal of the battery may be a display which is different from the display indicating that the battery is dead.
Such a display indicating the fact that the battery is dead or removed is maintained as it is unless it is rewritten. Therefore, the display indicating the fact that the battery is dead or removed is maintained, for example, even when the battery is replaced with a new one. In order to avoid such a situation, when an amount of energy equal to or greater than a predetermined value is detected after the battery is replaced, the display on the display unit is updated, for example, to display that the battery is sufficient, to display an initial screen at the time of activation or to display the screen which has been shown before the battery is replaced. This makes it possible to notify the user of the fact that power has been recovered by inserting a new battery.
Further, when the display unit employs plural display methods which consume different amounts of power, control can be performed such that a reduction of the amount of energy of the battery is detected at a point in time when the amount of energy is greater than an amount of energy at which a dead battery is detected and such that the display method of the display unit is switched to a method which results in smaller power consumption. This makes it possible to suppress power consumption of the battery and to thereby increase the life of the battery. When the display method of the display unit is switched, a display indicating that the battery has become low can be presented to warn the user. For example, a reduction in the amount of energy of the battery can be detected from the voltage of the battery, and control can be performed such that the battery voltage is compared with a first voltage at which a dead battery is detected and a second voltage higher than the first voltage and such that the display method of the display unit is switched to a method which results in smaller power consumption when the battery voltage drops below the second voltage.